The cores are wound by continuous cold rolled grain oriented silicon steel strip, then the cores are annealed in high temperature furnace. The manufacturing process make full use of grain orientation of silicon steels, so that the cores enjoy following advantages: Strong over-load capacity, low temperature rise, high efficiency, low managetic leakage, compact volume, low noise etc. And the cores are mainly used in toroidal transformer, current transducer, electrical transformer, ballest and so on.